Bi-directional overrunning clutch

ABSTRACT

A bi-directional overrunning clutch is disclosed for controlling torque transmission between a secondary drive shaft and secondary driven shafts. The overrunning clutch includes a pinion input shaft in a differential housing that engages with a clutch housing rotatably disposed within the differential housing. At least one race is located adjacent to the clutch housing and is engaged with an output shaft. A cage is located between the race and the clutch housing. The cage is movable with respect to the clutch housing. A first  coil is mounted within the differential housing adjacent to the cage and is adapted to produce an electromagnetic field when energized which causes the cage to drag with respect to the clutch housing. The dragging of the cage with respect to the clutch housing positions rolls within the cage to engage the clutch housing with the race when wheels on a primary drive shaft lose traction. A  If desired a second coil is  may be mounted within the differential housing adjacent adjacent  to the cage. The second coil is adapted to produce an electromagnetic field when energized which advances cage with respect to the clutch housing causing the clutch housing to engage with the races. When the second coil is activated, the output shaft drives the pinion input shaft producing engine braking. An electronic control system is utilized to control the energizing of the coils.

FIELD OF THE INVENTION

The present invention relates to clutches and, more particularly, to abi-directional electromechanical overrunning clutch for providing fourwheel drive capability.

BACKGROUND OF THE INVENTION

The increased demand in recent years for off-road and all terrainvehicles has led to tremendous developments in those types of vehicles.Many of the developments have centered around making the vehicle moreadaptable to changing road conditions, e.g., dirt roads, pavement andgravel. As the road terrain changes, it is desirable to vary the drivingcapabilities of the vehicle to more efficiently navigate the newterrain. Prior four-wheel drive and all terrain vehicles were cumbersomesince they required the operator to manually engage and disengage thesecondary drive shaft, e.g., by stopping the vehicle to physicallylock/unlock the wheel hubs. Improvements in vehicle drive trains, suchas the development of automated systems for engaging and disengaging adriven axle, eliminated many of the problems of the prior designs. Theseautomated drive systems are sometimes referred to as “on-the-fly” fourwheel drive. These systems, however, require the vehicle to be in either2-wheel or 4-wheel drive at all times.

Generally, all four-wheel drive vehicles include a differential fortransferring torque from a drive shaft to the driven shafts that areattached to the wheels. Typically, the driven shafts (or half shafts)are independent of one another allowing differential action to occurwhen one wheel attempts to rotate at a different speed than the other,for example when the vehicle turns. The differential action alsoeliminates tire scrubbing, reduces transmission loads and reducesundersteering during cornering (the tendency to go straight in acorner). There are four main types of conventional differentials: open,limited slip, locking, and center differentials. An open differentialallows differential action between the half shafts but, when one wheelloses traction, all available torque is transferred to the wheel withouttraction resulting in the vehicle stopping.

A limited slip differential overcomes the problems with the opendifferential by transferring all torque to the wheel that is notslipping. Some of the more expensive limited slip differentials usesensors and hydraulic pressure to actuate the clutch packs locking thetwo half shafts together. The benefits of these hydraulic (or viscous)units are often overshadowed by their cost, since they require expensivefluids and complex pumping systems. The heat generated in these systems,especially when used for prolonged periods of time may also require theaddition of an auxiliary fluid cooling source.

The third type of differential is a locking differential that usesclutches to lock the two half shafts together or incorporates amechanical link connecting the two shafts. In these types ofdifferentials, both wheels can transmit torque regardless of traction.The primary drawback to these types of differentials is that the twohalf shafts are no longer independent of each other. As such, the halfshafts are either locked or unlocked to one another. This can result inproblems during turning where the outside wheel tries to rotate fasterthan the inside wheel. Since the half shafts are locked together, onewheel must scrub. Another problem that occurs in locking differentialsis twichiness when cornering due to the inability of the two shafts toturn at different speeds.

The final type of differential is a center differential. These types ofdifferentials are used in the transfer case of a four wheel drivevehicle to develop a torque split between the front and rear driveshafts.

Many differentials on the market today use some form of an overrunningclutch to transmit torque when needed to a driven shaft. One successfuluse of an overrunning clutch in an all terrain vehicle is disclosed inU.S. Pat. No. 5,036,939. In that patent, the vehicle incorporatesoverrunning clutches directly into the wheel hubs, thus allowing eachwheel to independently disengage when required.

SUMMARY OF THE INVENTION

A bi-directional overrunning clutch is disclosed for controlling torquetransmission between a secondary drive shaft and secondary drivenshafts. The present invention, when used in a vehicle, provides fourwheel drive capability in the event of traction loss on any primarydrive shaft.

The overrunning clutch includes a differential housing with a pinioninput shaft extending outwardly from the housing. One end of the pinioninput shaft is engaged with the secondary drive shaft. The other end ofthe input shaft is located within the differential housing and includesan input gear. The input gear preferably engages with a ring gearrotatably disposed within the housing such that rotation of the inputgear produces concomitant rotation of the ring gear.

A clutch housing is attached to the ring gear and includes an inner camsurface. At least one and preferably two races are located adjacent tothe cam surface. Each race is engaged with an output shaft. The outputshaft, in turn, is engaged with a secondary driven half shaft.

A roll cage is located between the race and the cam surface. The rollcage has a plurality of slots which are preferably spaced equidistantlyabout its circumference. Each slot has a roll located therein. The rollcage is movable with respect to the clutch housing and the races.

A first armature plate is located adjacent to and engaged with the rollcage so that the first armature plate rotates in conjunction with theroll cage. A first coil is mounted within the differential housingadjacent the first armature plate. The first coil is adapted to producean electromagnetic field when energized which hinders the rotation ofthe first armature plate, thus causing the roll cage to drag withrespect to the clutch housing. The dragging of the roll cage withrespect to the clutch housing causes the rolls to engage the clutchhousing and the race when the wheels on the primary drive shaft losetraction. When traction loss occurs, the rolls become wedged between theclutch housing and the races so as to provide driving engagementtherebetween.

AIn one embodiment, a second armature plate is located adjacent the rollcage. A second coil is mounted within the differential housing adjacentto the second armature plate. The second coil is adapted to produce anelectromagnetic field when energized to hinder the rotation of thesecond armature plate. This causes the roll cage to advance with respectto the clutch housing causing the clutch housing to engage with theraces. In this mode of operation, the secondary driven half shafts andoutput shaft drive the pinion input shaft and secondary drive shaft,thereby producing engine braking.

In another embodiment, a third armature plate is located adjacent to theroll cage and a third coil is mounted within the differential housingadjacent to the third armature plate. The third coil produces anelectromagnetic field when energized which hinders the rotation of thethird armature plate. This causes the roll cage to move opposite thedirection of rotation of the clutch housing to assist in disengaging therolls from between the clutch housing and the races.

The clutch housing preferably has a plurality of toggle levers pivotallyattached thereto that engage with pins mounted on the roll cage. Theengagement between the toggle levers and the pins permits the roll cageto be advanced and retarded with respect to the clutch housing. Thesecond armature plate engages with the toggle lever to advance the cageand the third armature plate engages with the toggle lever to retard thecage.

The foregoing and other features and advantages of the present inventionwill become more apparent in light of the following detailed descriptionof the preferred embodiments thereof, as illustrated in the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show a formof the invention which is presently preferred. However, it should beunderstood that this invention is not limited to the precisearrangements and instrumentalities shown in the drawings.

FIG. 1 is a schematic representation of one drive train embodiment in avehicle incorporating the present invention.

FIG. 2 is a right side view of one embodiment of the bi-directionaloverrunning clutch according to the present invention.

FIG. 3 is cross-sectional view of the bidirectional overrunning clutchtaken along lines 3—3 in FIG. 2.

FIG. 4 is a cross-sectional view of the bi-directional overrunningclutch taken along lines 4—4 in FIG. 3.

FIG. 5 is an exploded view of the bi-directional overrunning clutchshown in FIGS. 2-4.

FIG. 6A is a schematic cross-sectional view of a roll cage in anon-activated position.

FIG. 6B is a schematic cross-sectional view of the roll cage in a firstposition.

FIG. 6C is a schematic cross-sectional view of the roll cage in anengaged position wherein the pinion input shaft drives the outputshafts.

FIG. 6D is a schematic cross-sectional view of the roll cage in a secondposition wherein the output shafts drive the pinion input shaft.

FIG. 7 is a cross-sectional view of a second embodiment of thebi-directional overrunning clutch showing use of toggle levers forcontrolling the roll cage.

FIG. 8 is a cross-sectional view of the second embodiment of thebi-directional overrunning clutch shown in FIG. 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numeralsillustrate corresponding or similar elements throughout the severalviews, FIG. 1 is a schematic representation of one embodiment of a drivesystem incorporating a bidirectional overrunning clutch 10 according tothe present invention. The drive system includes a transmission 12, aprimary drive shaft 14 a primary differential 16, and first and secondprimary driven shafts 18, 20 which drive primary wheels 22.

The drive system also includes a secondary drive shaft 24 which isrotatably connected to the bidirectional overrunning clutch 10 throughany conventional means known to those skilled in the art, such as asplined connection. The overrunning clutch 10, in turn, rotatably drivestwo secondary driven shafts 26, 28 which are attached to wheels 30.

The details of the bi-directional overrunning clutch will now bedescribed with respect to FIGS. 2 through 5. FIG. 2 illustrates theright cover 52 of the bi-directional overrunning clutch 10. Thesecondary drive shaft 24 engages with a splined end of a pinion inputshaft 32. The pinion input shaft 32 extends out from and is rotatablewith respect to a differential housing 34. More specifically, the pinioninput shaft 32 is located within a bearing assembly 36 that includes tworoller bearings 38 within a bearing support 40. The pinion input shaft32 is positioned against the inner race of the two roller bearings 38.The outer races of the bearings 38 lie against the bearing support 40.An oil seal 42 is also located between the bearing support 40 and thepinion input shaft 32. The oil seal 42 prevents oil from escaping out ofthe bearing assembly 36. The bearing assembly 36 is mounted within thedifferential housing 34 by any conventional means. A rubber O-ring 44 islocated between the bearing assembly 36 and the differential housing 24to provide a fluid tight seal.

The pinion input shaft 32 preferably has a bevel gear 46 formed on orattached to the end of the shaft 32 located within the differentialhousing 34. The bevel gear is preferably made from steel material withspiral bevels. The bevel gear 46 engages with a ring gear 48 locatedwithin the differential housing 34. The ring gear 48 is preferably madefrom steel with spiral bevels. In one embodiment of the invention, thering gear 48 and bevel gear 46 both have mating 35° spiral bevels. Thoseskilled in the art would appreciate that other angles can be used in thepresent invention depending on the design of the entire clutch systemand the anticipated loading. Furthermore, it is contemplated that othergearing arrangements, such as a worm gear set, may be used for engagingthe pinion input shaft 32 to the differential housing 34.

The ring gear 48 is preferably bolted to a clutch housing 50 which willbe described in more detail hereinafter. A right cover plate 52 islocated adjacent to the ring gear 48 and attached to the differentialhousing 34 though any conventional means, such as bolts. A thrustbearing 54 and thrust washer 56 are located between the right coverplate 52 and the ring gear 48. The thrust bearing 54 is in rollingcontact with the ring gear 48 and, in one embodiment, is a NTA-6074Torrington thrust bearing, sold by Torrington Co., Torrington, Conn. Thethrust washer 56 is located between the thrust bearing 54 and the rightcover plate 52 and is preferably made from steel. One suitable thrustwasher is a TRB-6074 Torrington thrust washer sold by Torrington Co. Thethrust bearing 54 and washer 56 combination allow the ring gear 48 tofreely rotate within differential housing 34. A rubber O-ring 58 ispreferably positioned between the right cover plate and the differentialhousing 34 to provide a fluid tight seal.

A bushing 60 is mounted between the clutch housing 50 and thedifferential housing 34, permitting the clutch housing 50 to freelyrotate within the differential housing 34. The bushing 60 is preferablya self-lubricating bushing made from composite material. One suitabletype of bushing is an MB 8540DU DU bearing sold by Garlock Bearing Inc.,Thorofare, N.J. The clutch housing 50 is preferably made from steelmaterial and has an inner cam surface which is discussed in more detailbelow. A roller assembly 62 is located within the clutch housing 50 andincludes a roll cage 64 which contains a plurality of rolls 66. The rollcage 64 preferably includes two independent sets of rolls 66 disposedwithin slots 68 formed in the roll cage 64 around its circumference. Inthe illustrated embodiment there are six rolls in each set of rolls. Theroll cage 64 is preferably made from hard anodized aluminum material.Alternatively, the roll cage 64 can be made from plastic or compositematerial. The rolls are preferably made from hardened steel material. Awire spring 70 retains the rolls 66 within the slots 68 of the roll cage64. The wire spring 70 is disposed within a groove 72 formed on theinner surface of the roll cage 64 and within depressions 74 formed inthe rolls 66.

Each set of rolls 66 is located adjacent to the inner cam surface of theclutch housing 50. The contour of the cam surface is shown in moredetail in FIGS. 6A through 6D and is configured with a plurality ofpeaks and valleys. When the roll cage 64 is located within the clutchhousing 50, the rolls 66 are located within the valleys with the camsurface tapering toward the race on either side of the roll 66(generally referred to herein as tapered portions 50 _(T)). The camsurface and rolls 66 provide the bi-directional overrunning capabilitiesas will be discussed hereinafter. Cam surfaces and roll cages inoverrunning clutches are well known in the art. See, e.g., U.S. Pat. No.4,373,407, which is incorporated herein by reference in its entirety.Hence, a detailed discussion of these features is not needed.

At least one and preferably two races 76 are rotatably located in thecenter of the roll cage 64. Each race 76 is adjacent one of the sets ofrolls 66 such that the outer surface of the race 76 contacts the set ofrolls 66. As will become evident hereinafter, the contact between therolls 66, the clutch housing 50 and the races 76 causes the races 76 torotate with the clutch housing 50. The races 76 are preferably made fromsteel material. A thrust bearing 77 is disposed between the two races 76to allow the races 76 to freely rotate with respect to one another. Thethrust bearing 77 is preferably an NTA-1828 Torrington thrust bearingsold by Torrington Co.

Each race 76 is engaged with a corresponding output shaft 78 through anyconventional means designed to transfer torque from the race 76 to theoutput shaft 78. In the illustrated embodiment, each race 76 includesinternal splines 80 which mate with external splines 82 formed on aportion of the output shaft 78. The splined arrangement illustratedpermits the output shaft 78 to be removed by sliding it axially out ofthe race 76. A shoulder 84 formed on the output shaft 78 limits theaxial translation of the output shaft 78 into the race 76. The outputshaft is preferably made from steel material. It is contemplated thatthe race 76 and output shaft 78 can be formed as an integral unit ifdesired. One of the output shafts 78 (i.e., the right output shaft)extends out of an opening 86 formed in the right cover plate 52. Aroller bearing 88 surrounds a portion of the output shaft 78 and engageswith the right cover plate 52. The roller bearing 88 supports the outputshaft 78 while permitting the output shaft 78 to rotate with respect tothe right cover plate 52. An oil seal 90 is preferably incorporated intothe right cover plate 52 around the output shaft 78 to provide a fluidtight seal between the two components.

Similarly, the other output shaft 78 (i.e., the left output shaft)extends out of an opening 92 formed in a left cover plate 94. A rollerbearing 96 surrounds a portion of the output shaft 78 and engages withthe left cover plate 94. An oil seal 98 is preferably incorporated intothe left cover plate 94 around the output shaft 78 to provide a fluidtight seal. The left cover plate 94 is attached to the differentialhousing 34 by any conventional means, such as bolts. A rubber O-ring 100is preferably inserted between the left cover plate 94 and thedifferential housing 34.

To assist in aligning the two output shafts 78, one of the output shafts78 preferably includes a raised protrusion 102 which mates with a recess104 formed in the other output shaft 78. A bushing 106 can be placed onthe protrusion 102 or in the recess 104 to facilitate relative motionbetween the two shafts.

The output shafts 78 extend outward from the differential housing 34 andconnect to secondary half shafts which drive the vehicle's wheels 30.Each output shaft 78 is connected to a secondary half shaft through anyconventional means known to those skilled in the art, such as a splinedconnection. (For the sake of simplicity, the output shafts 78 and twohalf shafts are collectively referred to herein as the secondary drivenshafts 26, 28.)

As discussed briefly above, the engagement of the rolls 66 with theclutch housing 50 and races 76 permits the transfer of torque from thesecondary drive shaft 24 to the secondary driven shafts 26, 28. In orderto activate the overrunning clutch, the present invention incorporatesan electromagnetic system. More specifically, the present inventionincludes two and more preferably three roll cage adjustment deviceswhich are electrically connected to an electronic control system. In onepreferred embodiment, the roll cage adjustment devices include aplurality of coils and armature plates. The coils and armature platesare mounted within the differential housing 34 to control the movementof the roll cage 64 with respect to the clutch housing 50.

A first coil 108 is located within a coil insert 110 which is mounted tothe right cover plate 52. The coil insert 110 is preferably made from ametallic material, such as steel or powdered metal, and is press fit orsimilarly attached to the housing. The first coil 108 is preferablyannular in shape with a central axis coincident with the axis ofrotation of the roll cage 64. The first coil 108 is preferably a bobbinwound coil which includes a plastic base about which the coil is wound.Suitable coils for use in the present invention are well known to thoseskilled in the electric clutch art. One satisfactory coil is disclosedin U.S. Pat. No. 5,036,939, which is incorporated by reference herein inits entirety. Other suitable coils are available from Endicot Coil Co.,Inc. Endicot, N.Y. The first coil 108 is bonded or otherwise attached tothe coil insert 110.

A first armature plate 112 is located between the first coil 108 and theroll cage 64. The first armature plate 112 is preferably annular inshape and is free to rotate with respect to the first coil 108 when thecoil is not energized. The first armature plate 112 includes at leastone and, more preferably at least three tangs or fingers 114 whichprotrude from the armature plate 112 toward the roll cage 64. The tangs114 engage with slots 116 formed in the roll cage 64. The first armatureplate 112 is locked to the roll cage 64 when the tangs 114 are engagedwith the slots 116. Hence, when the first coil 108 is not energized, thefirst armature plate 112 rotates with the roll cage 64. The firstarmature plate 112 is preferably made from steel material.

When the first coil 108 is energized, an electromagnetic field isgenerated between the first coil 108 and the first armature plate 112attracting the first armature plate 112 to the first coil 108 causing itto drag. Since the first armature plate 112 is engaged with the rollcage 64, the dragging of the first armature plate 112 causes the rollcage 64 to also drag or retard. In an alternate embodiment (not shown),the tangs 114 on the armature plate 112 do not engage with slots 116formed in the roll cage 64. Instead, the tangs 114 engage withprotrusions formed on the roll cage 64 when the first coil 108 isenergized.

Referring to FIGS. 4 and 5, the left side of the clutch housing 50 isshown with a plurality of dowel pins 118 extending outward from theclutch housing 50. A toggle lever 120 is pivotally mounted to each dowelpin 118. Each toggle lever 120 includes a fork at a radially inward end120 _(A) that is designed to engage with a cage pin 122 mounted on theroll cage 64. Pivoting of the toggle levers 120 about the dowel pins 118causes the forked ends 120 _(A) to urge the roll cage 64 to move (i.e.,advance or retard) with respect to the clutch housing 50. As such, theengagement and disengagement of the rolls 66 can be controlled bymanipulating the toggle levers 120. The radially outward end of eachtoggle lever 120 preferably includes an outer projection 120 _(B) asshown in the figure. The toggle levers 120 are preferably made fromsteel material and have a stepped thickness that varies fromapproximately {fraction (3/16)}th inch to {fraction (1/16)}th inch. Thedowel pins 118 are preferably made from steel material. The cage pins122 are also preferably made from steel material.

In order to control the pivoting of the toggle levers 120, the presentinvention incorporates second and third coils 124, 126 as shown in FIGS.4 and 5. The second coil 124 is mounted within a second coil insert 128which, in turn, is mounted to the left cover plate 94. The second coil124 preferably has an annular shape and is mounted to the left coverplate 94 on a central axis which is coincident with the axis of rotationof the clutch housing 50. A second armature plate 130 is located betweenthe second coil 124 and the toggle levers 120. The second armature plate130 is preferably annular in shape and has a plurality of tangs 132formed thereon that extend toward the toggle levers 120. The tangs 132are designed to contact or engage with the outer projections 120 _(B) onthe toggle levers 120. When the second coil 124 is energized, a magneticfield is generated that inhibits or limits the rotation of the secondarmature plate 130 (i.e., causing it to drag). As the clutch housing 50continues to rotate, the tangs 132 on the second armature plate 130contact the outer projections 120 _(B) on the toggle levers 120 urgingthe toggle levers 120 to pivot about the dowel pins 118. This causes theforked ends 120 _(A) of the toggle levers 120 to advance the roll cage64. As will be discussed in more detail below, the advancement of theroll cage 64 causes the rolls 66 to wedge between the tapered portions50 _(T) of the cam surface and the races 76. The second and third coils124, 126 are preferably similar to the first coil 108, and the secondand third coil inserts 128, 134 are preferably similar to the first coilinsert 110.

Similar to the second coil 124, the third coil 126 is mounted within athird coil insert 134 which is concentrically disposed within the secondcoil insert 128 and mounted to the left cover plate 94. The third coil126 is preferably annular in shape with a central axis that iscoincident with the axis of rotation of the clutch housing 50. A thirdarmature plate 136 is located between the third coil 126 and the togglelevers 120, and is substantially concentric with the second armatureplate 130. The third armature plate 136 preferably has a plurality oftangs 140 formed thereon that extend toward the toggle levers 120 andare configured to contact or engage with a portion of the forked ends120 _(A) of the toggle levers 120. When the third coil 126 is energized,a magnetic field is generated that inhibits or limits rotation of thethird armature plate 136. As the clutch housing 34 continues to rotate,the tangs 140 on the third armature plate 136 contact the forked ends ofthe toggle levers 120 causing the toggle levers 120 to pivot about thedowel pins 118 in a direction opposite from the direction of pivotingcaused by the second coil 124. The pivoting of the toggle levers 120result in the roll cage 64 moving in the opposite direction from thedirection of rotation of the clutch housing 50.

The coils 108, 124, 126 are connected to a electronic control system,such as a signal processor for controlling the energizing of the coils.(The electronic control system is generally identified by the numeral142 in FIG. 5.)

The operation of the bi-directional overrunning clutch will now bediscussed. Under normal operation (two-wheel drive mode), the electroniccontrol system 142 does not send any signals to energize the coils.Accordingly, the vehicle is propelled by the primary drive shaft 14 andprimary driven shafts 18, 20. The secondary drive shaft 24 rotates thepinion input shaft 32 which drives the ring gear 48. The ring gear 48rotates the clutch housing 50 within the differential housing 34. Sincethe coils are not energized, the springs 70 maintain the roll cage 64 ina relatively central or unengaged position (non-activated position).This position is best illustrated in FIG. 6A. In this position, therolls 66 are not wedged between the races 76 and the tapered portion 50_(T) of the cam surface of the clutch housing 50 and, therefore, thereis no driving engagement between the clutch housing 50 and the races 76.Instead, the rolls 66 and roll cage 64 rotate with the clutch housing50, independent from the output shafts 78. In this mode of operation,the secondary driven shafts 26, 28 do not drive the wheels but, instead,are driven by the wheels 30.

When it is desired to operate the vehicle such that four wheel drive isavailable when needed (four-wheel drive capability mode), the electroniccontrol system 142 is activated. Preferably, the activation is providedby manually actuating a button on the vehicle console, although thesystem can be automatically activated if desired. The electronic controlsystem 142 sends a signal to energize the first coil 108. (The secondcoil 124 and third coil 126 are not energized in this mode ofoperation.) The energizing of the first coil 108 creates anelectromagnetic field between the first coil 108 and the first armatureplate 112. The electromagnetic field causes the first armature plate 112to drag or slow in speed. Since the first armature plate 112 is engagedto the roll cage 64 by the tangs 114, the electromagnetic field causesthe roll cage 64 to slow with respect to the clutch housing 50 into afirst position. In this position (shown in FIG. 6B), the rolls 66 arelocated near to but not wedged between the tapered portion 50 _(T) ofthe cam surface and the races 76. Instead, the difference in rotationalspeed between the secondary drive shaft 24 and the output shafts 78maintains the rolls 66 in an overrunning mode. As such, the vehiclecontinues to operate in two-wheel drive (i.e., driven by the primarydrive shaft 14).

When the wheels 22 driven by the primary drive shaft 14 begin to slip,the rotational speed of the secondary drive shaft 24 and the outputshafts 78 begin to equalize relative to the ground, since ground speedcontrols four-wheel drive and overrunning engagement. As such, theclutch housing 50 starts to rotate faster than the output shafts 78 andraces 76. This change in relative speed between these components causesthe rolls 66 to wedge between the races 76 and the tapered portion 50_(T) of the cam surface (as shown in FIG. 6C). As a result, torque istransmitted from the clutch housing 50 to the races 76 and the vehicleis now operating in four-wheel drive (i.e., the primary driven shafts18, 20 and secondary driven shaft 26, 28 are driving the wheels 22, 30).The drive system will stay in four-wheel drive until the wheels 22 onthe primary drive shaft 14 stop slipping, at which point the outputshaft 78 once again overruns the clutch housing 50 and rolls 66disengage. The ability of the present invention to engage and disengagethe secondary driven shafts when needed allows the system to provideimmediate four-wheel drive capability in both forward and reardirections.

Another feature of the bi-directional overrunning clutch 10 according tothe present invention is that, even when the vehicle is operating infour-wheel drive capability mode, i.e., when torque is transmitted tothe secondary driven shafts 26, 28, the sets of rolls 66 canindependently disengage (overrun) from the clutch housing 50 whenneeded, such as when the vehicle enters into a turn and the wheel on onesecondary driven shaft 26 rotates at a different speed than the wheel onthe other secondary driven shaft 28. As such, the overrunning clutch 10provides the drive system with the advantages of an open differential incornering without traction loss, and the advantages of a lockingdifferential when in four-wheel drive without the disadvantages ofundersteering and tire scuffing when cornering.

The present invention also provides engine braking capability(backdriving mode) for use when driving the vehicle down steep inclines.In the backdriving mode, the secondary driven shafts 26, 28 are engagedwith the secondary drive shaft 24 and actually drive the secondary driveshaft 24. This is important since the front wheels generally have bettertraction than the rear wheels when the vehicle is descending down asteep slope in a forward direction. The present invention takesadvantage of this occurrence and engages the front wheels (via thesecondary driven shafts 26, 28 and output shafts 78) with the secondarydrive shaft 24 (via the clutch housing 50 and pinion input shaft 32)such that front wheels control the rotation of the secondary drive shaft24. This produces engine braking, thereby assisting in slowing down thevehicle.

The backdriving mode is controlled either by a traction sensor (notshown) which sends a signal to the electronic control system 142, ormanually engaged by the operator of the vehicle depressing a button (notshown) in the vehicle which sends a signal to the electronic controlsystem 142. The electronic control system 142 then energizes the secondcoil 124. (The first and third coils 108, 126 are not energized in thismode.) This creates a magnetic field that causes the second armatureplate 130 to slow or drag. The tangs 132 on the second armature plate130 contact the outer projections 120 _(B) on the toggle levers 120 asthe clutch housing 50 rotates causing the toggle levers 120 to pivotabout the dowel pins 118. As the toggle levers 120 pivot, the forkedends 120 _(A) of the toggle lever 120 urge the roll cage 64 to advance.This results in the rolls 66 becoming wedged between the races 76 andthe tapered portion 50 _(T) of the cam surface on the clutch housing 50(as shown in FIG. 6D). As such, the wheels 30 on the secondary drivenshafts 26, 28 are directly connected to the secondary drive shaft 24 andbecome the input to the gear box locking the entire gear train together.In this mode, both front wheels are engaged.

When in the backdriving mode, it is necessary to disengage the rolls 66from between the races 76 and the tapered portions 50 _(T) of the camsurface when the vehicle is no longer descending the hill. In order toaccomplish the disengagement, the electronic control system 142de-energizes the second coil 124 while energizing the first coil 108.The electromagnetic field generated by the first coil 108 inhibits orhinders the rotation of the first armature plate 112. Since the tangs114 on the first armature plate 112 are engaged with the slots 116 inthe roll cage 64, energizing the first coil causes the rolls 66 todisengage from between the races 76 and the tapered portions 50 _(T) ofthe cam surface.

It is contemplated that when in the backdriving mode, situations mayarise where the electromagnetic field produced by the first coil 108 maynot be sufficient to disengage the rolls 66 from between the races 76and the tapered portions 50 _(T) of the cam surface. In order to assistin disengagement, the electronic control system 142 also energizes thethird coil 126. This causes an electromagnetic field to form whichinhibits or limits the rotation of the third armature plate 136. Thetangs 140 on the third armature plate 136 contact the forked end 120_(A) of the toggle lever 120 providing additional leverage to pivot thetoggle lever 120 around the dowel pin 118. Depending on theconfiguration of the system, it may be desirable to add a fourth coiland a second toggle system to the right side of the clutch housing 50adjacent to the first coil 108 to provide additional release leverage.

While one preferred embodiment of the invention has been described withcoils and armature plates as the roll cage adjustment devices, thoseskilled in the art, in light of the teachings provided herein, wouldunderstand how to modify the invention to incorporate other mechanical,electrical, hydraulic or pneumatic devices in place of the coils and orarmature plates.

It is also contemplated that the cam surface need not be formed on theclutch housing but, instead, can be formed on the races. Also, theroller clutch described above can be easily modified to use spragsinstead of rolls. A person skilled in the art could readily make thesesubstitutions in light of the above teachings.

A second embodiment of the invention is shown in FIGS. 7 and 8 wherein atoggle system is incorporated into the right side of the differentialhousing 34. In this embodiment, the tangs 114 on the first armatureplate 112 do not engage with slots 116 formed in the roll cage 64.Instead, at least one, and more preferably three, toggle levers 200which are pivotally mounted to the clutch housing 50 and engaged withthe roll cage 64 for causing the roll cage 64 to advance and retard.

More particularly, each toggle lever 200 has an inner end 200 _(A) andan outer end 200 _(B). The outer end 200 _(B) is pivotally mounted tothe clutch housing 50 via a dowel pin 202. The toggle lever 200 also hasa slotted opening 204 located approximately midway along its length. Theslotted opening 204 is sized to slidingly engage with a protruding pin206 which extends outward from a flange 208. The flange 208, in turn, ismounted to the roll cage 64 by pins 210. Since the flange 208 is pinnedto the roll cage 64, it rotates with it. Furthermore, since the togglelevers 200 are pivotally attached to the clutch housing 50 and slidinglyengaged with the protruding pins 206, the roll cage 64 rotates with theclutch housing 50

The first armature plate 112 in this embodiment is configured with itstangs 114 located adjacent to the inner ends 200 _(A) of the togglelevers 200, similar to the third armature plate 136.

The operation of this embodiment of the overrunning clutch is similar tothe first embodiment described above. When it is desired to place thevehicle in four-wheel drive capability mode, the first coil 108 isactivated causing the armature plate 112 to drag. As the armature plate112 drags its tangs 114 contact the inner ends 200 _(A) of the togglelevers 200 causing the levers to pivot about the dowel pins 202. As thetoggle levers 200 pivot, they force the protruding pins 206 to retardthe roll cage 64. This places the rolls 66 in position to wedge betweenthe clutch housing 50 and the races 76 when the primary drive shaftloses traction. When the first coil 108 is deactivated, the armatureplate 112 is once again free to move. The natural motion of the wheelswill cause the rolls 66 to disengage from between the clutch housing 50and the races 76.

As discussed above, the first coil 108 is also activated when it isdesired to disengage the rolls 66 after engagement in the back drivingmode. In this situation, the activation of the first coil 108 causes thefirst armature plate 112 to drag. The tangs 114 on the armature plate112 engage the inner ends 200 _(A) of the toggle levers 200 and urgethem backward, out of their advanced position. This causes the roll cage64 to pull the rolls 66 out from engagement between the clutch housing50 and the races 76.

Other embodiments of the invention are also contemplated, such asmounting the three coils on the same side of the differential housing34. Hence, the exemplary embodiments described above should not beconsidered as limiting the full scope of the invention set forth in theclaims below.

Although the invention has been described and illustrated with respectto the exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention.

We claim:
 1. An overrunning clutch for controlling torque transmissionbetween a pinion input shaft and at least one output shaft, the clutchcomprising a differential housing; a pinion input shaft having an endrotatably disposed within the differential housing; at least one outputshaft having an end rotatably disposed within the differential housing;a roller clutch disposed within the differential housing and adapted tocontrol torque transmission between the pinion input shaft and the atleast one output shaft, the roller clutch having a first positionwherein the roller clutch is positioned to engage the pinion input shaftto the at least one output shaft to permit torque transmission from thepinion input shaft to the at least one output shaft, and a secondposition wherein the roller clutch engages the pinion input shaft withthe at least one output shaft to permit torque transmission from the atleast one output shaft to the pinion input shaft; and a firstelectromagnetic adjustment device mounted within the differentialhousing, the first electromagnetic device adapted to place the rollerclutch in its first position when energized; and a secondelectromagnetic adjustment device mounted within the differentialhousing, the second electromagnetic adjustment device adapted to placethe roller clutch in its second position when energized .
 2. Anoverrunning clutch according to claim 1 wherein the roller clutchincludes a clutch housing and a roll cage, and wherein the firstadjustment device includes a first coil which when energized drags theroll cage with respect to the clutch housing.
 3. An overrunning clutchaccording to claim 2 wherein the first electromagnetic device furtherincludes a first armature plate for engaging the roll cage, theenergizing of the first coil adapted to cause the armature plate to dragthe roll cage.
 4. An overrunning clutch according to claim 2 wherein theclutch housing has a plurality of toggle levers pivotally mountedthereon, each toggle lever engaged with the roll cage, the firstarmature plate adapted to pivot the toggle levers when the first coil isenergized to retard the roll cage.
 5. An overrunning clutch according toclaim 2 wherein the first armature plate includes tangs which engagewith slots formed in the roll cage.
 6. An overrunning clutch accordingto claim 2further comprising a second electromagnetic adjustment devicemounted within the differential housing, the second electromagneticadjustment device adapted to place the roller clutch in its secondposition when energized; and wherein the second adjustment deviceincludes a second coil which when energized advances the roll cage withrespect to the clutch housing.
 7. An overrunning clutch according toclaim 6 wherein the second electromagnetic device further includes asecond armature plate disposed between the coil and the roll cage, theenergizing of the second coil adapted to cause the second armature plateto advance the roll cage so that the roller clutch is in its secondposition.
 8. An overrunning clutch according to claim 7 wherein theclutch housing has a plurality of toggle levers pivotally mountedthereon, each toggle lever engaged with the roll cage, the secondarmature plate adapted to pivot the toggle levers when the second coilis energized to advance the roll cage.
 9. An overrunning clutchaccording to claim 8 wherein the third adjustment device includes athird coil which when energized pivots the toggle levers to retard theroll cage, the retarding of the roll cage moving the roller clutch outof its second position.
 10. An overrunning clutch according to claim 1wherein the overrunning clutch is mounted to a vehicle, the vehicleincluding a drive shaft and two half shafts, each half shaft having awheel engaged therewith, the overrunning clutch including two outputshafts, each output shaft being rotatably engaged with a half shaft, thepinion input shaft being rotatably engaged with the drive shaft, and anelectronic control system for controlling the electromagnetic adjustmentdevices device.
 11. An overrunning clutch according to claim 1 furthercomprising a second electromagnetic adjustment device mounted within thedifferential housing, the second electromagnetic adjustment deviceadapted to place the roller clutch in its second position whenenergized; and a third electromagnetic adjustment device mounted withinthe differential housing, the third electromagnetic adjustment deviceadapted to disengage the roller clutch from its second position when thethird electromagnetic device is activated.
 12. A bi-directionaloverrunning clutch for controlling torque transmission between a pinioninput shaft and at least one output shaft, the clutch comprising adifferential housing; a pinion input shaft having an end rotatablydisposed within the differential housing, the pinion input shaft adaptedto rotate an input gear located within the differential housing; a ringgear disposed within the housing and rotatably engaged with the inputgear; a clutch housing attached to the ring gear and rotatably disposedwithin the differential housing, the clutch housing having a cam surfaceformed on one side; at least one race disposed adjacent to the camsurface and engaged with an output shaft; a roll cage disposed betweenthe race and the cam surface, the roll cage including a plurality ofslots formed in and spaced circumferentially about the roll cage, eachslot having a roll located therein, the roll cage movable with respectto the clutch housing and the at least one race; a first armature platelocated adjacent to the roll cage; and a first coil mounted within thedifferential housing adjacent to the first armature plate, the firstcoil adapted to produce an electromagnetic field when energized whichhinders the rotation of the first armature plate causing the roll cageto drag with respect to the clutch housing; a second armature platelocated adjacent to the roll cage; and a second coil mounted within thedifferential housing adjacent to the second armature plate, the secondcoil adapted to produce an electromagnetic field when energized whichhinders the rotation of the second armature plate and causes the rollcage to advance with respect to the clutch housing, the advancement ofthe roll cage with respect to the clutch housing adapted to cause theclutch housing to drivingly engage with the at least one race .
 13. Abi-directional overrunning clutch according to claim 12 wherein thedragging of the roll cage with respect to the clutch housing positionsthe rolls so as to permit rotatable engagement between the at least onerace and the clutch housing for transmitting torque from the pinioninput shaft to the output shaft when the output shaft rotates at a speedsubstantially equal to the pinion input shaft.
 14. A bi-directionaloverrunning clutch according to claim 12 further comprising at least onetoggle lever pivotally mounted to the clutch housing, the at least onetoggle lever engaged with the roll cage such that pivoting of the atleast one toggle lever causes the roll cage to move with respect to theclutch housing; and wherein the first armature plate retards the rollcage by urging the at least one toggle lever to pivot.
 15. Abi-directional overrunning clutch according to claim 12 wherein thefirst armature plate includes tangs which engage with slots formed inthe roll cage.
 16. A bi-directional overrunning clutch according toclaim 12 wherein the advancement of the roll cage with respect to theclutch housing rotatably engages the at least one race to the clutchhousing such that the output shaft is drivingly engaged with the pinioninput shaft.
 17. A bi-directional overrunning clutch according to claim12 further comprising a second armature plate located adjacent to theroll cage; a second coil mounted within the differential housingadjacent to the second armature plate, the second coil adapted toproduce an electromagnetic field when energized which hinders therotation of the second armature plate and causes the roll cage toadvance with respect to the clutch housing, the advancement of the rollcage with respect to the clutch housing adapted to cause the clutchhousing to drivingly engage with the at least one race; at least onetoggle lever pivotally mounted to the clutch housing, the at least onetoggle lever engaged with the roll cage such that pivoting of the atleast one toggle lever causes the roll cage to move with respect to theclutch housing; and wherein the second armature plate advances the rollcage by urging the at least one toggle lever to pivot.
 18. Abi-directional overrunning clutch according to claim 17 wherein theengagement between the at least one toggle lever and the roll cage isprovided by at least one pin formed in the roll cage, the at least onetoggle lever having an end adapted to engage the pin in the roll cage.19. A bi-directional overrunning clutch according to claim 18 whereinthere are three toggle levers spaced substantially equidistant aroundthe clutch housing, each toggle lever includes an inner forked end whichmates with a corresponding pin formed on the roll cage, the pin beingcapable of moving within the forked end of the toggle lever.
 20. Abi-directional overrunning clutch according to claim 12 furthercomprising a second armature plate located adjacent to the roll cage; asecond coil mounted within the differential housing adjacent to thesecond armature plate, the second coil adapted to produce anelectromagnetic field when energized which hinders the rotation of thesecond armature plate and causes the roll cage to advance with respectto the clutch housing, the advancement of the roll cage with respect tothe clutch housing adapted to cause the clutch housing to drivinglyengage with the at least one race; a third armature plate locatedadjacent to the roll cage; and a third coil mounted within thedifferential housing adjacent to the third armature plate, the thirdcoil adapted to produce an electromagnetic field when energized whichhinders the rotation of the third armature plate and causes the rollcage to retard with respect to the clutch housing, the retarding of theroll cage with respect to the clutch housing adapted to disengage thedriving engagement between the clutch housing and the at least one race.21. A bi-directional overrunning clutch according to claim 20 furthercomprising at least one toggle lever pivotally mounted to the clutchhousing, the at least one toggle lever engaged with the roll cage suchthat pivoting of the at least one toggle lever causes the roll cage tomove with respect to the clutch housing; and wherein the third armatureplate retards the roll cage by urging the at least one toggle lever topivot.
 22. A bi-directional overrunning clutch according to claim 21wherein there are a plurality of toggle levers pivotally mounted to theclutch housing, each toggle lever having a first end which is engagedwith the roll cage and an outer projection formed on an end of thetoggle lever on the opposite side of the pivotal attachment from thefirst end, and wherein the second armature plate has a plurality oftangs formed thereon which project toward the roll cage, the secondarmature plate positioned within the differential housing so that thetangs are radially aligned with the outer projections on the togglelevers and adapted to contact the outer projections when the second coilis energized, the contact between the tangs and the outer projectionsadapted to cause the toggle lever to pivot.
 23. A vehicle having fourwheel drive capability comprising: a transmission; a primary drive shaftrotatably driven by the transmission; two primary half shafts rotatablyengaged with the primary drive shaft, each primary half shaft engagedwith a corresponding primary wheel; a secondary drive shaft rotatablyengaged with the transmission; an overrunning clutch assembly engaged tothe secondary drive shaft, the overrunning clutch assembly including: adifferential housing; a pinion input shaft rotatably disposed within thedifferential housing and engaged with the secondary drive shaft; aclutch housing disposed within the differential housing and rotatablyconnected to the pinion input shaft, the clutch housing having an innersurface; at least one race disposed adjacent to the inner surface of theclutch housing, the at least one race being engaged with an outputshaft; a cage disposed between the at least one race and the innersurface of the clutch housing, the cage having a plurality of slotsformed in and spaced circumferentially about the cage, each slot havinga movable member located therein, the cage being adjustable with respectto the clutch housing and the at least one race; a first armature platelocated adjacent to and adapted to engage with the cage; a first coilmounted within the differential housing adjacent to the first armatureplate, the first coil adapted to produce an electromagnetic field whenenergized which hinders the rotation of the first armature plate causingthe cage to move to a first position with respect to the clutch housing,the first position of the cage locating the movable members so as towedge between the inner surface and the at least one race when one ofthe primary wheels loses traction; a second armature plate locatedadjacent to the cage; a second coil mounted within the differentialhousing adjacent to the second armature plate, the second coil adaptedto produce an electromagnetic field when energized which hinders therotation of the second armature plate and causes the cage to move to asecond position with respect to the clutch housing, the second positionof the cage adapted to wedge the movable members between the innersurface and the at least one race; and an electronic control systemconnected to the first and second coils coil, the electronic controlsystem providing signals for controlling energizing of the first andsecond coils coil.
 24. A vehicle according to claim 23 wherein theoverrunning clutch further includes a second armature plate locatedadjacent to the cage; a second coil mounted within the differentialhousing adjacent to the second armature plate, the second coil adaptedto produce an electromagnetic field when energized which hinders therotation of the second armature plate and causes the cage to move to asecond position with respect to the clutch housing, the second positionof the cage adapted to wedge the movable members between the innersurface and the at least one race; and a third armature plate locatedadjacent to the cage; and a third coil mounted within the differentialhousing adjacent to the third armature plate, the third coil adapted toproduce an electromagnetic field when energized which hinders therotation of the third armature plate and causes the cage to move out ofthe second position and the movable members to disengage from betweenthe inner surface and the at least one race.
 25. A vehicle according toclaim 23 wherein the electronic control system includes a manuallyactuated button which when activated results in the energizing of thefirst coil.
 26. An overrunning clutch assembly comprising: adifferential housing; a pinion input shaft having an end rotatablydisposed within the differential housing; a clutch housing disposedwithin the differential housing and rotatably connected to the pinioninput shaft, the clutch housing having an inner surface; at least onerace disposed adjacent to the inner surface of the clutch housing, theat least one race being engaged with an output shaft; a cage disposedbetween the at least one race and the inner surface of the clutchhousing, the cage having a plurality of slots formed in and spacedcircumferentially about the cage, each slot having a movable memberlocated therein, the cage being adjustable with respect to the clutchhousing and the at least one race; a first armature plate locatedadjacent to and adapted to engage with the cage; and a first coilmounted within the differential housing adjacent the first armatureplate, the first coil adapted to produce an electromagnetic field whenactivated which hinders the rotation of the first armature plate causingthe cage to move to a first position with respect to the clutch housing,the first position of the cage locating the movable members so as to beadapted to wedge between the inner surface and the at least one race; asecond armature plate located adjacent to the cage; and a second coilmounted within the differential housing adjacent to the second armatureplate, the second coil adapted to produce an electromagnetic field whenactivated which hinders the rotation of the second armature plate andcauses the cage to move to a second position with respect to the clutchhousing, the second position of the cage adapted to wedge the movablemembers between the inner surface and the at least one race when theinner surface is rotating faster than the at least one race.
 27. Anoverrunning clutch according claim 26 further comprising a secondarmature plate located adjacent to the cage; a second coil mountedwithin the differential housing adjacent to the second armature plate,the second coil adapted to produce an electromagnetic field whenactivated which hinders the rotation of the second armature plate andcauses the cage to move to a second position with respect to the clutchhousing, the second position of the cage adapted to wedge the movablemembers between the inner surface and the at least one race.